Fiber Optic Cables Suitable for Automated Preconnectorization

ABSTRACT

Fiber optic drop cables are disclosed that are suitable for automated preconnectorization. In one embodiment, an optical waveguide is disposed in a buffer tube that has two strength components disposed on opposite sides thereof and a plurality of strength members. The plurality of strength members are disposed at a plurality respective interstices located between the buffer tube and the two strength components and shaped into a plurality of substantially triangular shapes for improving the balancing of the residual stresses in the fiber optic cable caused by the shrinkage of a cable jacket during cooling. In another embodiment, a fiber optic cable includes a tonable lobe connected by a web that is frangible and the web includes predetermined ratios for easily and reliable separation of the tonable lobe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/264,241,filed Nov. 1, 2005, the entire contents of which are hereby incorporatedby reference.

TECHNICAL FIELD

The present invention relates generally to fiber optic cables suitablefor routing optical fiber toward the subscriber such as fiber to thehome applications. More particularly, the present invention relates tofiber optic cables having separable toning lobes and/or that aresuitable in automated preconnectorization processes, although theinvention is not limited to such applications.

BACKGROUND

Communication networks are used to transport a variety of signals suchas voice, video, data transmission, and the like. Traditionalcommunication networks use copper wires in cables for transportinginformation and data. However, copper cables have drawbacks because theyare large, heavy, and can only transmit a relatively limited amount ofdata. On the other hand, an optical waveguide is capable of transmittingan extremely large amount of bandwidth compared with a copper conductor.Moreover, an optical waveguide cable is much lighter and smallercompared with a copper cable having the same bandwidth capacity.Consequently, optical waveguide cables replaced most of the coppercables in long-haul communication network links, thereby providinggreater bandwidth capacity for long-haul links. However, many of theselong-haul links have bandwidth capacity that is not being used. This isdue in part to communication networks that use copper cables fordistribution and/or drop links on the subscriber side of the centraloffice. In other words, subscribers have a limited amount of availablebandwidth due to the constraints of copper cables in the communicationnetwork.

As optical waveguides are deployed deeper into communication networks,subscribers will have access to increased bandwidth. Deployment ofoptical waveguides toward the subscriber is generally called fiber tothe location x (FTTx) applications and includes fiber-to-the-curb (FTTC)and fiber-to-the-home (FTTH) applications. There are certain obstaclesthat make it challenging and/or expensive to route optical waveguidescloser to the subscriber. For instance, making a suitable opticalconnection between optical waveguides is much more complicated thanmaking an electrical connection between copper wires. Additionally, asthe communication network pushes toward subscribers, the communicationnetwork requires more connections, which compounds the difficulties ofproviding optical waveguides to the premises of the subscriber. Thus,routing fiber optic cables towards the subscribers requires a quick andeasy solution for streamlining the installation process. Also, on theend of the network closest to the subscriber, smaller cables housingfewer optical fibers are typically used. Such cables have their own setof particular location, installation, termination, and connectorizationissues generally not found with long haul cables.

For example, fiber optic cables routed toward the premises of thesubscriber may be buried in the yard of the subscriber. Consequently,these buried fiber optic cables are preferably located and marked toprevent damage to the same before the subscriber or others dig.Generally speaking, the craft prefers dielectric cables since they donot have to be grounded and the like. However, dielectric cables aredifficult to locate when buried. To address this problem, fiber opticcables have included a toning wire for locating the buried cable. Thetoning wire is typically a conductor such as copper wire that can beused to locate the buried fiber optic cable by sending a signal alongthe toning wire that can be detected above ground to locate the cable.Specifically, the route of a buried fiber optic cable having a toningwire is found by attaching a tone generator device to an exposed portionof the toning wire so as to generate an electrical toning signal alongthe toning wire. A detector is then used by the craft to find the buriedportions of the toning wire by detecting the toning signal, therebyallowing marking of the cable location.

By way of example, U.S. Patent App. Pub No. 2005/0053342, the disclosureof which is incorporated herein by reference, discloses apreconnectorized fiber optic cable having a toning wire disposed in atoning lobe that is connected by a web to a main cable body. Thepreconnectorized cable includes a plug connector that allows the craftto quickly and reliably optically connect the cable. Before the plugconnector can be attached to the end of the cable the toning lobe mustbe separated from a portion of the main cable body.

However, conventional toning lobes may not have been as readily orreliably separable from the main cable body as desired. At times, duringseparation of the toning lobe from the main cable body, the cablesurface at the tear was not as smooth as desired after separating thetoning lobe. In extreme cases, the toning lobes may have undesiredseparation from the main cable body or the toning wires may beinadvertently torn from their lobes without the desired separation atthe web. In any event, leaving a poor tear and/or non-uniform surface atthe point of removal can cause problems during the preconnectorizationof the fiber optic cable. For instance, a poor tear or non-uniformsurface where the tonable wire was removed may require further attentionby the craft during connectorization to either remove the poorly tornsection and/or use additional sealing elements, etc., to ensureenvironmental sealing of the cable in the connector. This is especiallytrue for automated connectorization processes that require reliable andrepeatable separation performance of the toning lobe. Thus, improvedfiber optic cable designs incorporating a toning lobe that is easilyseparated from the main cable body without damage or leaving irregularsurfaces are desirable.

SUMMARY

One aspect of the present invention is directed to a fiber optic dropcable having a main cable body with at least one optical waveguidedisposed in a buffer tube, two strength components disposed on oppositesides of the buffer tube, and a plurality of strength members. Theplurality of strength members are disposed at a plurality of respectiveinterstices located between the buffer tube and the two strengthcomponents, wherein the plurality of strength members are shaped into aplurality of substantially triangular shapes. The substantiallytriangular shapes are useful for improving the balancing of the residualstresses in the fiber optic cable due to shrinkage of a cable jacketduring cooling.

Another aspect of the present invention is a fiber optic drop cablehaving a main cable body with at least one optical waveguide, at leastone strength component, and

a tonable lobe for locating the cable. The tonable lobe is connected tothe main cable body by a web that is frangible. The web has a firstradius R1 adjacent to the main cable body and a second radius R2adjacent to the tonable lobe and a radius ratio is defined as the ratiobetween the second radius and the first radius (R2/R1). The radius ratiois greater than about 1 and more preferably greater than about 2.

Yet another aspect of the present invention is directed to a fiber opticdrop cable having a main cable body having at least one opticalwaveguide disposed within a buffer tube, two strength componentsdisposed on opposite sides of the buffer tube, a plurality of strengthmembers, and a tonable lobe. The plurality of strength members beingdisposed at a plurality of respective interstices located between thebuffer tube and the two strength components. The strength members eachhave a substantially triangular shape for improving the balancing of theresidual stresses in the fiber optic cable due to shrinkage of a cablejacket during cooling. The tonable lobe is connected to the main cablebody by a web that is frangible and the web has a first radius R1adjacent to the main cable body and a second radius R2 adjacent to thetonable lobe. A radius ratio is defined as the ratio between the secondradius and the first radius (R2/R1), wherein the radius ratio is greaterthan 1.

The present invention is also directed to a fiber optic drop cablehaving a main cable body with at least one optical waveguide and atleast one strength component. A tonable lobe is connected to the maincable body by a web that is frangible. The web has a first thickness t1adjacent to the main cable body and the tonable lobe has a minimum wallthickness t3, wherein a tear control ratio is defined as the ratiobetween the minimum wall thickness and the first thickness (t3/t1). Thetear control ratio being greater than about 0.7.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention, and are incorporated into and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention, and together with the description serve to explain theprincipals and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one example of a fiber optic cableincorporating multiple aspects of the present invention.

FIGS. 1 a and 1 b depict cross-sectional views of fiber optic cablehaving uneven coupling of the cable jacket that can cause problems in anautomated preconnectorization process.

FIG. 2 is a schematic cross-sectional representation showing tip entryand die exit outlines of one example of a die head design useful forextruding cables as in FIG. 1.

FIG. 3 is a schematic cross-sectional representation of the die headdesign of FIG. 2 showing tip exit and die exit outlines.

FIG. 4 is an enlarged view of a portion of a cable similar to the cableof FIG. 1 showing the toning lobe and web portions in greater detail andidentifying certain parameters thereon.

FIG. 5 is a schematic representation of a testing jig used for measuringa separation force of a tonable lobe from the fiber optic cable of FIG.1.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Whenever possible, the same reference numeralswill be used throughout the drawings to refer to the same or like parts.With reference to FIG. 1, one example of a fiber optic cable 10according to the present invention will be described. Fiber optic cable10 includes an optical transmission component 15, at least one strengthcomponent 18, at least one strength member 20, and a cable jacket 22having a main cable body 23 and a toning lobe 28 that are connected by aweb 30. Web 30 is frangible for separating toning lobe 28 from maincable body 23 in a clean and reliable manner as discussed below, therebymaking cable 10 suitable for automated preconnectorization processes. Inthis cable, optical transmission component 15 includes a single opticalwaveguide such as an optical fiber 12 and a buffer tube 14, but otherconfigurations of the optical transmission component are possible. Forinstance, optical transmission component 15 may include multiple opticalfibers or the buffer tube may be eliminated such as in a tubelessconfiguration. Optical fiber 12 can be any type of optical fiberincluding, for example, a single-mode, multi-mode or dispersion shiftedoptical fiber. Likewise, optical transmission component 15 may includetight-buffered fibers, fiber bundles, fiber ribbons or other opticalfiber configurations/groupings. In this cable, buffer tube 14 is sizedto contain up to twelve optical fibers 12, but only a single opticalfiber is depicted. Specifically, buffer tube 14 has a nominal outerdiameter D1 of about 3.0 millimeters and an inner diameter of about 1.8millimeters, but other suitable diameters such as smaller diameters arepossible for other suitable fiber counts. The inner diameter is sized toaccommodate a suitable excess fiber length (EFL) for the desired tensileand contraction windows for the intended fiber count. Additionally,buffer tube 14 may also house at least one waterblocking and/orwater-swellable substance 16, for example, a gel, thixotropic grease,and/or a water-swellable tape, thread, or yarn for inhibiting themigration of water within buffer tube 14. Buffer tube 14 may be formedfrom a suitable polymer such as polypropylene, polyethylene, PVC and/orblends thereof.

As shown, cable 10 has two strength components 18 and four strengthmembers 20, thereby providing a flexible cable design having the desiredtensile rating with a relatively small cross-sectional footprint. Thecombination of strength components 18 and strength members 20 allowscables of the present invention to withstand the predetermined tensileloads and yet have a suitable overall bending flexibility, while stillmaintaining a relatively small cross-sectional footprint. Stated anotherway, cable 10 has an improved flexibility compared with another cablehaving the same tensile rating without the strength members since theGRPs would have to be larger making the cable stiffer and which may alsoincrease the cross-sectional footprint. Consequently, cable 10 providesthe craft with a cable having the desired tensile strength withoutsurpassing a desired maximum level of cable stiffness, thereby allowinga cable to be bent or coiled to a predetermined radius of curvature asrequired for installation, slack storage, and the like.

Specifically, strength components 18 are relatively stiff rods such asglass reinforced plastic (GRPs) that provide the main source ofanti-buckling strength and tensile strength, whereas strength members 20are tensile yarns that generally lack anti-buckling strength but providea significant amount of tensile strength. Strength components 18 mayoptionally include a water-swellable coating or the like disposedthereon for inhibiting the migration of water along the cable. Strengthmembers 20 are tensile yarns that provide tensile strength, butgenerally lack anti-buckling strength and generally speaking do notresist bending. Strength members 20 may be formed from a group offiberglass strands, aramid fibers or other suitable tensile yarns, andmay also include a superabsorbent material thereon for inhibiting themigration of water along the cable. By way of example, strengthcomponents 18 are GRP components having a rod-like shape with a diameterof about 1.6 millimeters and strength members 20 are 800 tex fiberglassyarns, but other suitable materials may be used for either the strengthcomponents and/or strength members. In this example, each of the fourindividual strength members 20 has about 20% of the tensile strengthrating of one of the strength components. In other words, the totaltensile strength rating of all four strength members 20 is about 80% ofone of the strength components 18.

During the manufacture of cable 10 the coupling of cable jacket 22around the other cable elements can occur unevenly, thereby resulting inuneven or unbalanced residual stresses in cable jacket 22 due toshrinkage of a cable jacket during cooling. Generally speaking, couplingrefers to load transfer mechanism that enables certain cable componentsto act as a composite structure, which is generally caused by the radialshrinkage of the jacket during cooling. In other words, shrinkage of thecable jacket in the radial direction enables coupling of certain cablecomponents. It has been discovered that uneven coupling occurs when thestrength components and/or the strength members are not uniformlylocated about optical transmission component 15 along the length ofcable 10. Uneven coupling can cause bending or deflection of the end ofthe cable when cut. For instance, cable 10 will have uneven coupling ofcable jacket 22 when the surface area of the optical transmissioncomponent contacting cable jacket 22 is non-uniform on opposing sidesand/or changes along the length of the cable.

Illustratively, FIGS. 1 a and 1 b depict explanatory cross-sectionalviews of fiber optic cables similar to cable 10 having unbalanced cablejacket coupling. FIG. 1 a depicts a cable 10′ where the strength members20 on the right-side of the optical transmission component have migratedto cover a larger area thereof compared with the left-side of theoptical transmission component. Consequently, the coupling of the cablejacket with the optical transmission component on the right-side isreduced compared with the left-side since it has been covered by thestrength members that have spread out to cover a larger area of theoptical transmission component. FIG. 1 b depicts a cable 10″ where thetop strength member 20 on the left-side of the cable has migrated aboutstrength component 18 on the left-side. Again, this reduces the couplingof the cable jacket on the left-side of the cable compared with theright-side of the cable. Consequently, when cables 10′ or 10″ are cutthey will deflect or bend to relieve the unbalanced residual stressesdue to the unbalanced coupling.

Generally speaking, the cables shown in FIGS. 1 a and 1 b performadequately with respect to the intended use even with the unbalancedresidual stresses caused by uneven coupling of the cable jacket;however, such unbalanced residual stresses can be troublesome for theautomation of cable preconnectorization. Specifically, when the cable iscut to length for connectorization or the like, it may deflect or bendin an unpredictable manner due to localized release of the residualstresses due to unbalanced coupling. In other words, any unbalancedresidual stresses residing in the cable jacket are allowed to actlongitudinally adjacent to the cut end of the cable, thereby causing thecable to deflect or bend unpredictably. Such unpredictable deflectionsor bending of the cable may pose problems during an automatedconnectorization process since the location of the cable end/cablecomponents will vary. Thus, one embodiment of the present invention,generally balances the strength members and strength components aboutthe optical transmission component so that the cable may be cut withoutcausing undue deflection or bending of the cable end, thereby aidingautomation of cable preconnectorization. Suitable shapes andorientations of the above tensile components, in particular afterextrusion, will be discussed below. Of course, the concepts of thepresent invention can be practiced with cables designs that do notinclude the toning lobe such as a cable similar to cable 10 but withoutweb 30 and attached toning lobe 28. Likewise, cables employing theconcepts of the present invention can have other shapes beside thegenerally flat configuration of cable 10, i.e., having end sections 24that are generally arcuate and a pair of generally flat-side sections26.

As shown in FIG. 1, strength members 20 are formed in four locationswithin cable 10. Specifically, strength members 20 are disposed withininterstitial spaces between buffer tube 14 and strength components 18 ina compact manner. Before cable manufacture is completed, the strengthmembers have a generally rectangular cross-sectional shape. For example,strength members 20′ may have cross-sectional dimensions of about 0.25millimeters by about 2.5 millimeters when passing into the extrusiontooling as generally shown by FIG. 2. During manufacture, strengthmembers 20 are shaped in the die head to the desired shape as shown incable 10 of FIG. 1. As shown, the four strength members 20 are disposedin the interstices with a substantially triangular shape aftermanufacture, thereby allowing relatively even coupling of the cablejacket with the other cable components. Consequently, when an end ofcable 10 is cut for connectorization, the bending or deflection of theend is reduced compared with the cables shown in FIGS. 1 a and 1 bbecause the unbalanced residual stress is reduced.

Cable 10 may be manufactured by operation of pressure extrusion tooling,using an exemplary die and tip design as schematically illustrated inFIGS. 2 and 3. However other methods and structures may also be used tomanufacture the cable of FIG. 1 and variations thereof described herein.As schematically depicted in FIGS. 2 and 3, the extrusion toolingextrudes jacketing material about the strength components 18, strengthmembers 20, optical transmission component 15, and a toning wire 32 asthe components are fed into the tooling. As the cable components are fedinto the extrusion tooling, a jacketing compound, e.g., polyethylene orother suitable compound, is supplied under suitable temperature andpressure conditions to the tooling. The jacketing compound generallysurrounds the cable components thereby forming cable jacket 22therearound. Of course, cable jacket 22 may be formed from othersuitable thermoplastics, such as a medium density polyethylene (MDPE),polypropylene, PVC, or the like. By way of example, cable jacket 22 hasa width w1 of about 8-9 millimeters, a width w2 of toning lobe 28 andweb 30 of about 2-3 millimeters, and a height of about 4-5 millimeters.Of course, other suitable dimensions are possible for the cable jacket.

Specifically, FIG. 2 shows a cross-section of a tip entrance profile 40superimposed on an outline of the die exit 42. FIG. 3 shows across-section of a tip exit profile 44 superimposed on the die exitprofile. For purposes of this disclosure, die exit profile 42 isconsidered coextensive with the outer surface of cable 10, although someshrinkage in jacket material is to be expected during cooling. Oneskilled in the art is able to fine tune the tip and die profiles asneeded to achieve the various designs disclosed herein without undueexperimentation, taking into account typical jacketing materialshrinkages, tolerances, etc.

During travel through the tooling and in particular the die tip, thevarious cable components are placed so as to achieve the orientation ofcable components shown in FIG. 1. In particular, strength members 20 arecompressed from the generally rectangular shape into substantiallytriangular shapes, within interstices between buffer tube 14 andstrength components 18. Of course, the substantially triangular shape ofthe strength member can have some variation in shape while stillproviding generally balanced coupling such as conforming to the roundshape of buffer tube 14 and respective strength components 18 onrespective sides. In FIG. 2, four such strength members 20′ are shownwithin tip entrance profile 40 prior to compression within the tip toachieve the shape and orientation within tip exit profile 42. It shouldbe understood that variations in the number and shape of strength memberyarns 20′, as well as changes to tip profiles 40 and 42, are possiblewithin the scope of the present invention.

One or more of the following attributes may be achieved duringextrusion. For example, strength components 18 are located generallyadjacent to the optical transmission component and preferably contactthe same, thereby allowing for a cable having a compact cross-sectionalfootprint. Further, strength members 20 are placed in interstitial areasbetween buffer tube 14 and strength components 18. Strength members 20are generally in contact with buffer tube 14 and an adjacent strengthcomponent 18 so as to form a substantially triangular shape thatconforms to the sides of buffer tube 14 and strength component 18.Additionally, the respective centers of strength components 18 andbuffer tube 14 are preferably generally aligned along an X-X axis,thereby creating a preferential bend characteristic for the cable.

As shown in FIG. 1, the shape of strength members 20 is substantiallytriangular as it is placed into the interstice, however, such shape isnot required for all aspects of the invention since other cableconfigurations are possible such as using strength components havingshapes other than round. Also, it is noted that strength members 20 aregenerally speaking symmetrically disposed about the buffer tube oroptical component and do not extend all the way around opticaltransmission component 15, thereby influencing the coupling of cablejacket 22 therewith. Specifically, a top portion 46 and a bottom portion47 (hereinafter portions 46,47) of buffer tube 14 contact cable jacket22 directly. As depicted, portions 46, 47 extends through about the samerespective angles along the buffer tube or the optical component. Incable 10, the respective angles are about 45 degrees about thecircumference of buffer tube 14, although in other configurations theangles may vary. Preferably, portions 46 and 47 are substantially equalin size and symmetrical in location about the buffer tube or opticalcomponent for purposes of uniform coupling of cable jacket 22. As shownin FIG. 3, tip exit profile 44 is generally constructed to form strengthmembers 20 into the desired shape, i.e., substantially triangular, whilemaintaining a pair angles α and β are about equal so that portions 46,47in cable 10 end up about equal. In other words, the tooling inhibits thestrength members from migrating out of their desired positions and/orshapes.

In preferred embodiments, strength members 20 do not extend beyond (upand down as shown in FIG. 1) buffer tube 14 toward side sections 26 ofcable 10, but may extend therebeyond by design and/or in manufacturingvariation. Consequently, the preferred embodiments have minimumjacketing thickness requirements that are defined by the diameter D1 ofbuffer tube 14. Were strength members material to extend beyond buffertube 14 so as to become the outermost element (vertically, as shown),then additional jacketing material may be required, at least adjacentstrength members 20, to form a minimum jacket thickness. If a uniformlyflat side section 26 were desired, then the additional thickness wouldgenerally extend along the entire side sections 26. The illustratedcable construction of FIG. 1 thus uses less jacketing material and/orallows for a smaller cable cross-sectional footprint (i.e., the cableheight is reduced). Also, allowing jacketing material to contact buffertube 14 at points 46 and 47 allows for coupling that is beneficiallyimproved for automation of preconnectorization and/or uniformlydistributed along the cable, thereby inhibiting the unpredictablebending or deflection of the cable when cut.

It may also be noted that strength members 20 are in contact with lessthan 180 degrees of the circumference about strength components 18. Inother words, strength components 18 are in contact with the jacketingmaterial for more than 180 degrees of the circumference of the strengthcomponents. As above, increasing the amount of strength component 18 incontact with jacket 22 aides in improving the evenness of coupling ofthe jacketing material, thereby leading to more uniform residualstresses within the cable and inhibiting the deflection or bending ofthe resulting cable when cut. Also, symmetry along horizontal andvertical axis (as shown in FIG. 1) of the location of strength members20 in interstitial spaces between strength components 18 and buffer tube14, as well as symmetry of locations of buffer tube 14 and strengthcomponents 18 relative to each other, also helps provide for more evencoupling within the cable.

It should be understood however, that each and every characteristicabove is not required to practice the concepts of the present invention,whether related to strength element design, shapes, and/or location asdescribed above, or whether related to toning lobe and web design asdescribed below.

The orientation of cable components 15, 18, and 20 within jacket 22 isachieved by virtue of the tip entrance and exits shown in FIGS. 2 and 3.Thus, the various elements are fed into the tip and the reduced size ofthe opening within the tip squeezes the elements together in a desiredconfiguration. While it is impossible as a practical matter to perfectlyalign such cable components entirely uniformly along an entire cable,one of skill in the art can design tooling achieve the resultingorientation as shown in FIG. 1, in view of the disclosures related toFIGS. 1-3.

As stated above, it would be possible to modify the structure above invarious ways to modify their attributes of the resulting cable product.For example, two strength members 20′ could be used instead of four,with a portion of the strength members being disposed between strengthcomponents 18 and buffer tube 14. Also, instead of the opticaltransmission component shown, different optical transmission componentsor structures may be used. Also, depending upon the desired tensile andbending characteristics, the relative diameters of the strengthcomponents and the size and amount of strength member material usedcould be varied to achieve desired ratings. Additionally, in certainsituations, nonsymmetrical designs could be used, for example using onlyone strength component 18 or differing numbers and or placements ofother cable components.

Turning now to FIG. 4, an enlarged view of toning lobe 28 and web 30 ofa cable similar to cable 10. Specifically, the enlarged view of FIG. 4is similar to cable 10 except it depicts a concentricity error of thetoning wire with the tonable lobe as may occur during manufacturing.FIG. 4 also illustrates certain dimensions related to these portionsthat can influence tear performance so that toning lobe 28 and web 30are reliably and cleanly separated from an end portion 24 of cable 10with the application of a predetermined separation force. Moreover, thepreferred separation force for the toning lobe prevents an excessiveseparation force while inhibiting inadvertent separation during cablebending, coiling, and the like. Preferably, the separation force isbetween about 10 Newtons and about 50 Newtons for the desiredperformance and more preferably between about 15 Newtons and about 30Newtons. The separation force is measured as the toning lobe is pulledaway from the main cable body along the X-X axis as shown in FIG. 1;however, the toning lobe may be separated by pulling in otherdirections. As shown in FIG. 5, a preferred way of measuring theseparation force uses a testing jig (not numbered) that routes thetoning lobe portion being pulled about a sheave 50 that rotates.Additionally, the testing jig allows the cable to move in a directiongenerally perpendicular to an applied force F as it is applied duringseparation. Thus, the force measured is the separation force appliedalong the X-X axis.

As shown in FIG. 4, cable 10 has a first radius R1 that is definedbetween end portion 24 and base portion 48 of web 30. A second radius R2is defined between distal portion 50 of web 30 and lobe 28. According toone aspect of the present invention selecting a predeterminedrelationship between R1 and R2, i.e., a radius ratio of R2/R1, improvesthe separation of web 30 and toning lobe 28 from end portion 24. FIG. 4also shows a first thickness t1, a second thickness t2, and a thirdthickness t3. First thickness t1 is the thickness at the base portion 48of web 30, second thickness t2 is the thickness at the distal portion 50of web 30, and third thickness t3 is a thickness of lobe 28 near R2.Third thickness t3 is measured at a point of a minimal wall thickness 52facing end section 24, measured radially outwardly from the center ofwire 32 generally in the direction of arcuate section 24 of main cablebody 23. Third thickness t3 is a point at which stresses will increaseduring the separation of toning lobe 28 and web 30 from main cable body23. If toning wire 32 is perfectly concentrically located within toninglobe 28, then t3 is the difference in radii between toning lobe 28 andthe toning wire 32. However, toning wire 32 is not always concentricallydisposed within toning lobe 28 in a manufactured cable. By way ofexample, FIG. 4 shows toning wire 32 having a concentricity error withrespect to toning lobe 28 so that thickness t3 is not the difference inradii between toning lobe 28 and toning wire 32. Generally speaking, theconcentricity error can occur during the normal manufacture of cable 10and can affect the separation/tear performance.

Aspects of the present invention involve selecting a predeterminedrelationship of certain combinations of thicknesses t1, t2 and t3(either along with or separate from the R1 and R2 relationship) forimproving the separation of web 30 and toning lobe 28 from end portion24 from main cable body 23. By way of example, the desired reliable andclean separation of toning lobe 28 and web 30 along base portion 48 ismore likely to occur when t2 is greater than t1, i.e., a thickness ratiot2/t1 is greater than unity. Also, it has been determined that desiredseparation of toning lobe 28 and web 30 at base portion 48 is morelikely to occur if a tear control ratio t3/t1 is greater than about 0.7,thereby inhibiting tearing along the minimal thickness portion 52 wheret3 is measured. Likewise, if R2 is greater than R1, (i.e. the radiusratio of R2/R1 is greater than unity) web 30 is more likely to be tornat base portion 48 rather than another location on the web towards thedistal portion 50 when the separation force is applied.

Stated numerically, preferably the tear control ratio t3/t1 is greaterthan 0.7; more preferably, the ratio is greater than about 0.74; and,most preferably the ratio is greater than about 0.81. Also, for thedesired separation performance, the thickness ratio t2/t1 is greaterthan about 1.0, and more preferably greater than about 1.10, and mostpreferably greater than about 1.15. Moreover, for desired separation,the radius ratio R2/R1 is greater than about 1.0, more preferably about2.0 or greater, and most preferably about 4.0 or greater. It should beunderstood that all of these relationships need not be satisfiedsimultaneously according to the scope of the present invention toachieve improved separation of the web and toning lobe from the maincable body.

The above stated parameters tend to induce stress concentrations in thedesired location (across base 48), leading to desired separationperformance. This desired separation performance is especiallyadvantageous in automated preconnectorization applications, but is alsoadvantageous for separation by hand. Simply stated, the above mentioneddimension ratios inhibit stretching and/or tearing of web material inundesired locations (and/or tearing out of the toning wire from thetoning lobe) and instead concentrates the tearing stress at base 48,thereby achieving separation/tear characteristics resulting in areliable and clean separation. Thus, an uneven distribution of stressacross base portion 48 whereby, for example, high stresses are inducedalong a surface of base portion 48 and relatively lower stresses areinduced across the central portion of base portion 48 may not producethe desired tear, in particular if higher and more evenly distributedstresses are induced at distal portion 50 or a minimum wall thickness52. However, the separation performance may be a function of more thanone parameter, for instance, the same value of the tear control ratiot3/t1 may perform differently based on varying other web dimensionsand/or toning lobe dimensions.

Illustratively, table 1 below includes information regarding a number ofexemplary simulated, iterative designs using suitable modeling softwarein which R1, R2, t1, and t2 parameters were set and the t3 parameter wasiteratively varied, so as to investigate the affect the tear controlratio t3/t1. In the simulated design, toning lobe 28 had an outerdiameter (not labeled) of 1.0 millimeter with a 24 AWG copper wire andthe length 1 of web 30 was 0.5 millimeters. As depicted in Table 1,different values of the ratios of t2/t1 and R2/R1 can influence thevalues for “acceptable” and “unacceptable” separation performance. Arating of “acceptable” means the simulated model indicated tearing atweb base portion 48 and a rating of “unacceptable” means the simulatedmodel indicated tearing at minimum wall thickness 52. Additionally,further iteration could identify a more precise cross-over between thetwo values for each tear control ratio t3/t1, meaning the acceptableratio for each set of parameters wherein tearing is at the desired baseportion 48 is likely between the acceptable and unacceptable valuesshown in Table 1. Likewise, the other ratios may perform differentlybased on varying other web dimensions and/or toning lobe dimensions.

TABLE 1 t3/t1 T2/t1 R2/R1 Acceptable Unacceptable 1.11 3.00 0.81 0.771.17 10.00 0.78 0.75 1.15 5.00 0.75 0.71 1.13 8.33 0.70 0.67 1.10 1.200.77 0.73 1.03 1.20 0.77 0.74 1.09 2.00 0.74 0.70 1.03 2.00 0.74 0.71

Of course, other suitable dimensions and/or combinations of dimensionsmay be used to arrive at a cable having a suitable separationperformance. In one preferred embodiment, toning wire 32 is a 24 AWGcopper wire having a diameter of about 0.5 millimeters, toning lobe 28has an outer diameter (not labeled) of about 1.7 millimeters, and web 30has a length 1 of about 0.9 millimeters. In this embodiment, the length1 was about 0.9 millimeters (almost double of the simulated model) toallow a sufficient amount of cooling water to contact web 30 duringmanufacture, thereby aiding in generally uniform cooling and inhibitingdeformation of the extruded shape. Tooling was designed and a cable wasmanufactured according to this preferred embodiment dimensions so thatit had suitable separation/tear characteristics, thereby making itsuitable for an automated preconnectorization process. Specifically, thedimensions of a cross-section of the manufactured cable were examinedand measured. One skilled in the art understands that variations inmanufacturing, shrinkage and the like can cause the same cable or othercables manufactured using the same tooling to have other values whenmeasured at different cross-sections along the cable. Typical values forthe cross-section of the manufactured cable were examined and measuredas follows, R2 was about 0.25 millimeters and R1 was about 0.05millimeters for a radius ratio of R2/R1 of about 5; t2 was about 0.6millimeters and t1 was about 0.3 millimeters for a thickness ratio oft2/t1 or about 2.0; and t3 was about 0.3 millimeters for a tear controlratio t3/t1 of about 1.0. Cables of the present invention can have othersuitable dimensions for the toning lobe, toning wires, and/or web,thereby resulting in different ratios.

As utilized herein, R1 and R2 refer to a radius of curvature at theillustrated locations. It is recognized, however, that the radius ofcurvature of complex shapes often varies, either according to a formula(for example along an ellipse) or otherwise in two or three dimensions.Therefore, the radius of curvature discussed herein is not limited tocircular, arcuate two-dimensional shapes. Also, the radius of curvatureillustrated applies generally to the identified region (i.e., along thebase portion 48 of web 30), not just at the exact point illustrated. Thesame concepts apply to the thicknesses t1, t2, and t3 as to localizedtwo- and three-dimensional variation. Therefore, it is within the scopeof the invention to utilize the radius and thickness informationdiscussed herein in various ways within and along the portions of thestructures discussed. Moreover, FIG. 4 illustrates that the web 30 isgenerally symmetrical about the X-X axis (FIG. 1); however, the web mayoptionally be asymmetric about the X-X axis. By way of example, web 30and toning lobe 28 can be designed to have preferential tear direction(i.e., the web 30 prefers to tear in one direction) by using differentradii on the one side of the X-X axis. For instance, the values of R1and R2 on the opposing side of the X-X axis can be larger to create apreferential tear direction for web 30. The preferential tear directioncan be marked with an indicia 33 such as a stripe, protrusion in theextrusion or the like. Likewise, web 30 can optionally include a ripstop 35 of increased material disposed periodically along the length ofweb 30 for inhibiting the tear from propagating unless a sufficientforce is provided. Rip stop 35 can be formed along the cable bypulsating the extrusion at the web or in other suitable ways as known toone skilled in the art.

Also, persons of ordinary skill in the art will appreciate thatvariations and modifications of the foregoing embodiments may be madewithout departing from the scope of the appended claims. For example,optical transmission component may comprise at least one tight bufferedfiber and/or a bundle of optical fibers. As an alternative to glassreinforced plastic, strength components can be metallic or aramid fibersimpregnated with a suitable plastic material so as to provide addedstiffness. Although a circular cross section for strength components anda substantially triangular cross section for strength members 20 aredisclosed, other cross sectional shapes may be used as well. Theconcepts described herein can be applied to many cable designs, forexample, self-supporting, buried, indoor, and indoor/outdoor cableapplications. Flame retardant jacket materials can be selected toachieve plenum, riser, or LSZH flame ratings. Also additional waterblocking protection can be added. For example, at least onewater-swellable tape or yarn (not shown) can be disposed adjacent to theoptical transmission component. Cables according to the presentinvention may also include at least one electrical conductor for poweror data transmission, for example, at least one coaxial or single wire,or a twisted pair of wires. Ripcords and/or an armor layer can be addedadjacent buffer tube 14.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A fiber optic drop cable comprising: a main cable body, the maincable body having at least one optical waveguide, at least one strengthcomponent, and a cable jacket; and a tonable lobe, the tonable lobehaving a toning wire that includes a copper material for locating thefiber optic drop cable, the tonable lobe being connected to the cablejacket of the main cable body by a web that is frangible, wherein theweb has a first radius R1 adjacent to the main cable body and a secondradius R2 adjacent to the tonable lobe, and a radius ratio is defined asthe ratio between the second radius and the first radius (R2/R1),wherein the radius ratio is greater than
 2. 2. The fiber optic dropcable of claim 1, the main cable body further comprising at least onestrength member.
 3. The fiber optic drop cable of claim 2, the at leastone optical waveguide being disposed within a buffer tube.
 4. The fiberoptic drop cable of claim 3, the buffer tube having a thixotropic greasetherein.
 5. The fiber optic drop cable of claim 2, the web having afirst thickness t1 adjacent to the main cable body and a secondthickness t2 adjacent to the tonable lobe and a thickness ratio isdefined as the ratio between the second thickness and the firstthickness (t2/t1), wherein the thickness ratio is greater than
 1. 6. Thefiber optic drop cable of claim 2, the main cable body having a width ofabout 10 millimeters or less and a height of about 5 millimeters orless.
 7. The fiber optic drop cable of claim 1, the optical waveguidebeing housed in a buffer tube, the main cable body having two strengthcomponents and a plurality of strength members disposed at a pluralityinterstices between the buffer tube and the two strength components. 8.The fiber optic drop cable of claim 7, the plurality of strength membersbeing shaped into a plurality of substantially triangular shapes forimproving the balancing of the residual stresses in the fiber opticcable due to shrinkage of a cable jacket during cooling.
 9. The fiberoptic drop cable of claim 2, the web having a first thickness t1adjacent to the main cable body and the tonable lobe having a minimumwall thickness t3, wherein a tear control ratio is defined as the ratiobetween the minimum wall thickness and the first thickness (t3/t1),wherein the tear control ratio is greater than about 0.7.
 10. The fiberoptic drop cable of claim 2, the tonable lobe having a separation forcefrom the main cable body between about 10 Newtons and about 50 Newtonsalong a X-X axis.
 11. A fiber optic drop cable comprising: a main cablebody, the main cable body having at least one optical waveguide, atleast one strength component, and at least one strength member; and atonable lobe, the tonable lobe having a toning wire that includes acopper material for locating the fiber optic drop cable and the tonablelobe being connected to the main cable body by a web that is frangible,wherein the web has a first thickness t1 adjacent to the main cable bodyand the tonable lobe has a minimum wall thickness t3, and a tear controlratio is defined as the ratio between the minimum wall thickness and thefirst thickness (t3/t1), wherein the tear control ratio is greater thanabout 0.7.
 12. The fiber optic drop cable of claim 11, the web having afirst radius R1 adjacent to the main cable body and a second radius R2adjacent to the tonable lobe and a radius ratio is defined as the ratiobetween the second radius and the first radius (R2/R1), wherein theradius ratio is greater than
 1. 13. The fiber optic drop cable of claim12, the radius ratio being greater than about 2.0.
 14. The fiber opticdrop cable of claim 11, the main cable body having two strengthcomponents and a plurality of strength members disposed at a pluralityof interstices between a buffer tube and the two strength components.15. The fiber optic drop cable of claim 14, the strength members beingshaped into a plurality of substantially triangular shapes for improvingthe balancing the residual stresses in the fiber optic cable due toshrinkage of a cable jacket during cooling.
 16. The fiber optic dropcable of claim 11, the at least one optical waveguide being disposedwithin a buffer tube.
 17. The fiber optic drop cable of claim 16, thebuffer tube having a thixotropic grease therein.
 18. The fiber opticdrop cable of claim 11, the web having a first thickness t1 adjacent tothe main cable body and a second thickness t2 adjacent to the tonablelobe and a thickness ratio is defined as the ratio between the secondthickness and the first thickness (t2/t1), wherein the thickness ratiois greater than
 1. 19. A fiber optic drop cable comprising: a main cablebody, the main cable body having at least one optical waveguide, atleast one strength component, and at least one strength member, the maincable body having a width of about 10 millimeters or less and a heightof about 5 millimeters or less; a tonable lobe, the tonable lobe havinga toning wire that includes a copper material for locating the fiberoptic drop cable and the tonable lobe being connected to the main cablebody by a web that is frangible, wherein the web has a first thicknesst1 adjacent to the main cable body and the tonable lobe has a minimumwall thickness t3, wherein a tear control ratio is defined as the ratiobetween the minimum wall thickness and the first thickness (t3/t1),wherein the tear control ratio is greater than about 0.7.
 20. The fiberoptic drop cable of claim 19, the tonable lobe having a separation forcefrom the main cable body between about 10 Newtons and about 50 Newtonsalong a X-X axis.